1. Field of the Invention
The present invention relates to a driver circuit, and more particularly, to a driver circuit of a display device.
2. Description of the Related Art
Techniques of manufacturing a semiconductor device, for example, a thin film transistor (TFT), which has a semiconductor thin film formed on an inexpensive glass substrate, have been making rapid progress in recent years. This is because there is an increasing demand for active matrix liquid crystal display devices (liquid crystal display devices).
In the active matrix liquid crystal display device, several hundred thousands to several millions of TFTs are arranged in matrix in a pixel portion, and electric charges going into and out of pixel electrodes that are connected to each TFT are controlled by the switching function of the TFTs.
Conventionally, thin film transistors employing an amorphous silicon film formed on a glass substrate are arranged in the pixel portion.
Further, in recent years, a structure is known in which quartz is utilized as a substrate and thin film transistors are manufactured from a polycrystalline silicon film. In this case, both a peripheral driver circuit and a pixel portion are constructed of the thin film transistors formed on the quartz substrate.
Still further, recently, also known is a technique in which thin film transistors using a crystalline silicon film are formed on a glass substrate by laser annealing or other techniques. Employment of this technique allows a pixel portion and a peripheral driver circuit to be integrated on the glass substrate.
Active matrix liquid crystal display devices are mainly used in notebook personal computers. Different from analog data used in the current television signals (NTSC or PAL) or the like, the personal computer outputs digital data to a display device. Conventionally, digital data from a personal computer are converted into analog data and then inputted into the active matrix liquid crystal display device, or to an active matrix liquid crystal display device that utilizes an externally attached digital driver.
Therefore, a liquid crystal display device having a digital interface capable of directly inputting digital data from outside is in the spotlight.
Here, a portion of a source driver of the liquid crystal display device having a digital interface that is recently in the spotlight is shown in FIG. 17. In FIG. 17, reference numeral 8000 denotes a shift register circuit and reference numeral 8100 denotes a digital data latch circuit. The shift register 8000 generates a timing signal on the basis of a clock signal (CLK), a clock back signal (CLKB), and a start pulse (SP) which are supplied from outside, and then sends out the above timing signal to the digital data latch circuit 8100. Based on the timing signal from the shift register circuit 8000, the digital data latch circuit 8100 samples (takes in) and stores and holds digital data inputted from outside.
Note that a scanning direction switching circuit is included in the shift register circuit 8000 shown in FIG. 17. The scanning direction switching circuit is a circuit for controlling the order of the output of the timing signal from the shift register circuit 8000 from left to right or from right to left in accordance with a scanning direction switching signal inputted from outside.
In a conventional shift register circuit such as the shift register circuit 8000 shown in FIG. 17, the shift register circuit 8000 is complicated and constructed by a large number of elements. In the present situation in which an active matrix liquid crystal display device with higher resolution is demanded, the surface area of the shift register circuit becomes larger as its resolution is improved. Thus, the number of elements constructing the shift register circuit is also increased.
Because of this increase in the number of elements, the production yield in the entire liquid crystal display devices becomes worse. Further, if the possessed surface area of the circuits becomes larger, it hinders the making of small scale liquid crystal display devices.